feat: allow customize isProd function

[Jeff-Tian]

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

在碰到错误时，有一个判断是否为生产环境的逻辑 isProd，目前不能被自定义。故添加了自定义这个逻辑的功能，望采纳！

默认逻辑是看 app.config.env，如果不是 local 或者 unittest，就认为是正式生产环境，然而多数现实情况下，除了 local 和 unittest ，还有多个环境，比如：

• dev
• test
• stage
• prod
• canary
• qa
  等等。很可能我们希望 dev 和 test 不算作正式环境（可以暴露原始错误堆栈信息）。

通过允许在 onerror 配置中自定义这个逻辑，可以让以上需求实现起来比较简单。

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[popomore]

我们认为非本地环境都是在服务器部署的，行为应该一致，这个不应该被修改。

[Jeff-Tian]

默认是这样，但应允许改写，保持灵活 获取 Outlook for Android<https://aka.ms/ghei36>

…

________________________________ From: Haoliang Gao <[email protected]> Sent: Monday, August 26, 2019 6:25:02 PM To: eggjs/egg-onerror <[email protected]> Cc: Jeff <[email protected]>; Author <[email protected]> Subject: Re: [eggjs/egg-onerror] feat: allow customize isProd function (#30) 我们认为非本地环境都是在服务器部署的，行为应该一致，这个不应该被修改。 ― You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub<#30?email_source=notifications&email_token=AAZWHDDBR5VRDDSF2PZQLE3QGOVP5A5CNFSM4ILJBP5KYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOD5D67BI#issuecomment-524808069>, or mute the thread<https://github.com/notifications/unsubscribe-auth/AAZWHDDSWBPHA7Q5DDXBQQ3QGOVP5ANCNFSM4ILJBP5A>.

[hyj1991]

Duplicated with #33.